Patch antennas or so-called microstrip antennas have been known for a long time. They generally comprise an electrically conductive base surface, a dielectric carrier material arranged thereabove and an electrically conductive effective surface provided on the upper side of the dielectric carrier material. The upper effective surface is generally excited by a feed line extending transversely to the above-mentioned planes and layers. A coaxial cable is primarily used as the connection cable, the external conductor of which is electrically connected at a connection to the ground conductor, whereas the internal conductor of the coaxial cable is electrically connected to the effective surface located at the top.
A tunable microstrip antenna is known, for example, from U.S. Pat. No. 4,475,108. Integrated varactor diodes are used for frequency tuning in this patch antenna.
The use of varactor diodes for tuning an antenna is, however, basically also known from the publication IEEE “Transactions on antennas and propagation”, September 1993, Rod B. Waterhouse: “Scan performance of infinite arrays of microstrip patch elements loaded with varactor diodes”, pages 1273 to 1280.
The use of an optically controlled pin diode for frequency tuning is to be inferred, as known, from the prior publication IEEE “Transactions on antennas and propagation”, September 1993, A. S. Daryoush: “Optically tuned patch antenna for phased array applications”, 1986, pages 361 to 364. It is located in a plane of the patch surface and connects this to an additional coupling surface.
A very similar principle in this respect is basically also to be inferred from U.S. Pat. No. 5,943,016 A and U.S. Pat. No. 6,864,843 B2. The fact that introduced capacitors can be used for frequency tuning, which are, for example, incorporated in a patch, is known from U.S. Pat. No. 6,462,271 B2. A very complex mechanical tuning of the patch antenna may, however, also be inferred as known according to the prior publication IEEE “Transaction on antennas and propagation”, S. A. Bokhari, J-F Züricher: “A small microstrip patch antenna with a convenient tuning option”, November 1996, volume 48, pages 1521 to 1528.
Independently of the aforementioned patch antennas, multi-layer antennas of planar construction are also known, for example, as so-called “stacked” patch antennas. The possibility exists by means of such an antenna type to increase the band width of an antenna of this type or to ensure resonances in two or more frequency ranges. The antenna power gain can also be improved by antennas of this type.
The disadvantage in all previously known antenna arrangements of this type is the comparatively complex construction.
In the case of the previously known tunable antennas mentioned at the outset, a series of further components is generally necessary, which frequently even have to be directly integrated into the patch antenna. This generally requires not only a more complex development, but frequently also leads to an increase in the production costs.
Moreover, the previously known measures for achieving a tunable patch antenna can frequently also not be applied or transferred to conventional commercial ceramic patch antennas.
Finally, the above-mentioned previously known patch antennas also have the disadvantage that although they propose measures for frequency tuning, the proposed measures generally are not used for influencing the antenna pattern.
In comparison, we provide an improved tunable antenna of planar construction in which with comparative low outlay, not only frequency tuning, but primarily influencing of the antenna pattern is possible. In this case, it should preferably be possible to produce the antenna according to the invention using conventional commercial patch antennas.
Numerous advantages can be realized with the solution we provide.
Numerous advantages can be realized with the solution according to the invention.
An important advantage is produced in that influencing of the antenna pattern is possible with the antenna in a simple manner without a considerable outlay for additional components that are complicated to produce under certain circumstances, or even only a fine tuning, being necessary. Expensive special development or expensive production of additional parts is therefore avoided. However, the fact that in the scope of the invention, conventional commercial patch antennas, above all conventional commercial ceramic patch antennas can be used, emerges above all as an important advantage. When they are used in the scope of the invention, these do not have to be specially changed, but only completed in the context of the invention, producing a very economical overall construction. In this case, a frequency tuning and also an influencing of the antenna pattern are possible in the scope of the invention.
This is all the more surprising as the effective structure provided at the top on the patch antenna may have a longitudinal and transverse extension, which is greater, or which at least partially covers the edge of the effective surface located underneath and extends beyond the edge of the effective surface. It would be, in fact, to be expected in a case such as this, that the patch surface located at the top would disadvantageously influence the radiation pattern.
In a preferred embodiment of the invention, the metal structure located over the patch antenna may not only have a larger dimensioning in the longitudinal and transverse direction than the patch antenna located underneath. Deformations, openings etc. may at least also be configured in this metal structure. It is even possible for this metal structure to be divided into individual metal structural elements and/or regions, which are, for example, not connected to one another mechanically and/or electrically.
However, it is provided according to the invention that the metal structure is connected at least via an electrical connection to the ground surface, wherein this electrical connection may be a galvanic connection, a capacitive, serial and/or a connection, which is produced using electrical components and assemblies. Thus, in a preferred embodiment of the invention, the mentioned conducting or conductive structure may thus be connected by means of at least one electrical connection with the interposition of at least one electrical component to the ground surface. The electrical connection between the ground surface and the metal structure above the patch antenna, may thus take place as mentioned by direct contact or else by using any electrical components to thereby influence the property of the antenna. Possible examples here are varactor diodes, which represent a current-controlled capacitor. The patch antenna can therefore be tuned with regard to its frequency.
In a particularly preferred embodiment of the invention, the mentioned electrical connection between the metal structure and the ground surface is formed using carrying feet or support feet, on which an electrically conductive line is configured or which are themselves electrically conductive. The support feet or the at least one support foot is to this extent also formed from a metal structure, which, for example, can be connected in one piece with the metal structure above the patch antenna and may be produced merely by stamping and canting.
A plurality of support devices, which preferably simultaneously form the electrical connection to the ground surface optionally by using further electrical parts and components, are preferably provided in the peripheral direction of the metal structure. In the case of an n-polygonal design of the metal structure, n-feet are preferably provided. If the metal structure is rectangular or square, a corresponding, preferably electrically conductive support foot is thus preferably provided on each side, preferably in the central region. If the metal structure is divided into different part structures, a support foot, which is in turn preferably electrically conductive, is at least also preferably provided for each electrically conductive part structure.
Instead of the metal structures, one generally electrically non-conductive structure may also be provided, for example in the form of a dielectric body, which is covered with a correspondingly conductive layer.
In a development of the invention, the electrically conductive structure, in other words the so-called metal structure, is in this case formed, for example, by a copper surface on a printed-circuit board. The printed-circuit board could be metallized here, for example, on the upper side, whereas the electrical components (for example a varactor diode) are placed on the lower side. The carrying feet preferably provided as the carrying device could, for example, be connected to delimited areas of the upper printed-circuit board metallizing and be guided by means of through-platings to the electric components. Alternatively, the electrical components could also be located on the upper side of the printed-circuit board.
Although the patch antenna according to the invention also has a further additional conductive structure at a spacing with respect to the effective surface located at the top, this is nevertheless not a “stacked” patch antenna in the conventional sense, as, in stacked patch antennas, the patch surface provided at the top (in other words the additional effective surface in question) is not contacted via a conductive connection with the ground surface.